I suspect there is something in SP1 (maybe related to SSTP or NAP?) that the PPP servers at Verizon do not like. I've even changed around all the normal PDANet PPP settings to not use LCP extensions and other settings but this always remains the same:

I can get a connection and browse with PDANet 1.80 and Vista SP1 for about 10 seconds and then the connection drops and disconnects rather harshly.

Rollback to RTM Vista and it works fine.

I've even disabled the SSTP IP Helper in Device Manager, no go.

For now when I am on the road and without a net connection, I've been booting up an XP SP3 virtual machine in VMWare using the USB-passthru and connecting that way. I use a loopback adapter on Vista that makes the host machine a client of the XP VM's ICS. It is a very esoteric setup I will admit, but I at least can get some network connectivity to my Vista host machine this way.

XP SP3 should be noted - it makes me think the SSTP/NAP stuff might not be the overall issue causing the connection failures.

I am too having the same/very similar issue with my Samsung i760 and Vista SP1. I have uninstalled and reinstalled SP1 with the same outcome. PdaNet responded with a vague answer for me to enable some dial and remote services but that also fixed nothing. I know of others with the same phone and SP1 who don't have any issues though.